Session
Identifiers 
As opposed to stateless HTTP requests, which can always be routed to any server determined by any load-balancing scheme, stateful requests have to be sent to the specific server that holds the corresponding session context. Unique session identifiers are used to establish a mapping between the session and its associated state stored on the server.
There are different kinds of SAP session identifiers used to uniquely identify user sessions residing on either the Application Server ABAP or the Application Server Java on a specific instance. Note that in order to differentiate between ABAP and Java applications, the SAP Web Dispatcher uses a database table of all known ABAP URL-prefixes.
Session identifiers can be represented in the HTTP header as cookies or as part of the URL in order to enable stateful sessions without cookies (URL-rewriting scheme).
Some session identifiers contain the name of the server which holds the session context. Other session identifiers do not contain the server name. For those session identifiers a shared memory table (session ID table) is used for always dispatching one session identifier to the same server.
More Information
For more information about the different identifiers, see